1. Field of the Invention
The present invention relates to a connecting device connecting a spray boom to a chassis or to an element secured to the chassis of an agricultural sprayer.
2. Discussion of the Background
A connecting device such as this is known to those skilled in the art. Specifically, patent application FR 2 759 544 describes an agricultural sprayer comprising, among other things, a chassis equipped with wheels and a number of spray nozzles arranged at substantially regular intervals along a boom. During work, said boom is deployed transversely to a direction of forward travel of said sprayer and said nozzles spray a product onto plants that are to be treated. In this prior-art document, said boom is connected to said chassis by means of two identical parallelograms which extend in approximately vertical respective planes. Said parallelograms can be deformed by means of a respective hydraulic ram. This deformation of the parallelograms allows said boom to be shifted with respect to said chassis, mainly in a vertical direction, so as to adapt the spraying height of said nozzles to the taller or shorter size of the plants to be treated. In this document, said parallelograms are arranged symmetrically on each side of a vertical mid-plane of said sprayer, and the supply circuits for said rams are connected up in parallel.
With such a connecting device, various factors mean that in practice said parallelograms do not deform at the same speed. In consequence, said boom, as it is shifted with respect to said chassis, will become inclined with respect to a horizontal plane by pivoting about a longitudinal axis of said sprayer. As a result, the spray height of said nozzles is no longer uniform, which is detrimental to the correct distribution of said product over the plants treated. In addition, when the boom moves away from said horizontal plane, the distribution of the weight of said boom between the two parallelograms is no longer symmetric, this distribution being to the detriment of the lowermost parallelogram. This difference in loading between the parallelograms further exacerbates the difference between said deformation speeds, hence making the phenomenon worse. This results in very heavy stresses on the various pivot points and on the various arms that make up the connecting device and, in the case of sprayers with a wide span, there is even the risk that said boom might strike the ground.
Experience has also shown that a device with two parallelograms, such as the one described in this earlier document, does not afford satisfactory rigidity in the face of stresses orthogonal to said vertical mid-plane. Indeed what happens is that when working on sloping ground, for example, or more generally when said sprayer is running over uneven ground, said boom is often found to flap undesirably with respect to said chassis in a direction transverse to said direction of forward travel. This flapping in turn places significant and repetitive stress on said pivot points that make up the connecting device, and also disrupts the correct distribution of said product over the plants treated.
The two observations described hereinabove have led those skilled in the art to strengthen this known connecting device, for example by joining the two parallelograms together using crossmembers.
However, this stiffening makes the operations of mounting said connecting device harder. In addition, it leads to an increase in the mass of the assembly and to an increase in the cost of manufacture which is already hampered by the use of two hydraulic rams.
The object of the present invention therefore aims to overcome the various drawbacks of the state of the art by producing a connecting device which is less expensive to manufacture and easier to mount while at the same time having good mechanical behaviour.
The objective assigned to this invention is achieved by means of a connecting device characterized in that it consists of a single quadrilateral arranged in a plane which is substantially vertical and substantially parallel to the longitudinal plane of the sprayer.
Indeed, the use of such a device makes it possible to reduce considerably, by comparison with the state of the art, the number of parts needed for making the connection between a spray boom and a chassis of an agricultural sprayer or an element secured to said chassis, hence making the assembly easier to mount and the construction less expensive.
Another feature of the invention consists in using just one ram to deform this device, hence yielding an even greater drop in the cost of manufacture.
Another feature of the invention lies in the fact that this quadrilateral is made up of a carrying arm and of an orienting arm. Said carrying arm is intended to take most of the stress applied by the spray boom, whereas the orienting arm has the single function of keeping the orientation of a plane in which said boom extends substantially vertical. Thus, the distribution of load between the carrying arm and the orienting arm is set. It is therefore easy to optimize the shape of these arms to guarantee correct dynamic behavior of the boom.